Multi-stage eductor apparatus

ABSTRACT

A multi-stage eductor apparatus includes a first stage eductor with an inlet, an outlet, and a venturi throat between the inlet and outlet into which a driving fluid is injected to flow from the outlet and create a suction at the inlet for drawing material into the inlet and through the first stage eductor with the driving fluid, and at least a second stage eductor of the same or similar configuration, with the inlet of the second stage eductor connected directly to the outlet from the first stage eductor, thereby increasing the suction at the inlet to the first stage eductor and maintaining the suction at the inlet to the first stage eductor through a wide range of driving fluid flow rates.

RELATED APPLICATION DATA

This application claims the benefits of U.S. Provisional Patent Application Serial No. 60/492,084, filed Aug. 1, 2003, and titled Multi-Stage Eductor Apparatus.

FIELD OF THE INVENTION

The present invention generally relates to venturi-type suction devices and apparatus, and in its preferred embodiments more specifically relates to suction and mixing eductor devices and apparatus utilizing a plurality of longitudinally aligned stages.

BACKGROUND OF THE INVENTION

The venturi tube, which invented by Giovanni Venturi, basically comprises two tapered sections of pipe joined by a narrow throat. This convergent-divergent shape is commonly referred to as a diffuser when used in venturi tubes. As a fluid flows through the venturi tube structure the fluid velocity in the throat is increased and the pressure is reduced, in keeping with the principles of conservation of energy and with Bernoulli's Theory, which states, “At any point in a pipe through which a fluid is flowing the sum of the pressure energy, the kinetic energy, and the potential energy of a given mass of the fluid is constant.”

Over time it was realized that the reduced pressure section of the venturi structure provided suction capabilities that could be put to use. Thus, a solid, liquid or gas could be moved, aerated, pumped, mixed, entrained, reacted, transferred, conveyed, agitated, sheared, or blended with a venturi tube incorporating an opening at the point of greatest suction or vacuum. The absence of any moving parts in the venturi-based suction device provides significant advantages in reliability and operation as compared to, e.g., mechanical pumps.

There are many names for venturi tubes that incorporate a suction port. For example, if the motive or driving fluid is a liquid, it is normally referred to as an eductor. If the motive or driving fluid is a gas such as steam, the venturi tube is commonly referred to as an ejector. Two other common names are aspirator and siphon pump or siphon. However, the venturi tube with a suction port is almost universally referred to as a jet pump or venturi jet. For the sake of brevity and consistency, the remainder of the disclosure of the present invention will utilize the term eductor, and it is to be understood that the term “eductor” as used herein shall refer to any venturi structure regardless of the motive fluid used or the purpose for which the suction is utilized.

When an eductor is used to produce a suction for material transport, mixing, etc., the motive fluid is typically injected at or just before the narrowed throat of the venturi structure, so that the motive fluid will increase in velocity as it flows through the venturi throat, reducing pressure and creating a suction. Since the motive fluid is injected tangentially, the longitudinal path into the throat is available for the free flow of other material in response to the suction created by the device. That material then becomes mixed with and entrained by the driving fluid in the throat of the venturi structure.

Various designs for the injection of the motive fluid have been developed. In one design, manufactured by the Derbyshire Machine and Tool Company of Philadelphia, Pa., nozzles are located on the periphery of the inlet to the diffuser. Derbyshire refers to its design as the Peri-Jet® Eductor. As another example, an eductor with a lobed shape jet nozzle is manufactured by Vortex Ventures, Inc. of Houston, Tex. Vortex Ventures refers to its eductor as the LobeStar® Mixing Eductor. This nozzle is disclosed in U.S. Pat. No. 5,664,733, to Gerald Lott.

There are several drawbacks associated with eductors known in the prior art. First, an eductor has a specific geometry with respect to the jet nozzle diameter, the throat, the diffuser, the suction inlet and the discharge outlet. The geometry or diameter of the jet nozzle determines the mass flow rate of the driving fluid. The throat diameter of the diffuser section determines the velocity of the combined streams which are the driving fluid and the entrained material. The geometry of the divergent section of the diffuser determines the pressure recovery capabilities of the eductor.

Specific geometries can be referred to as fixed geometries. Quite simply, eductors operate with pump curves based upon flow rate through the jet nozzle at a specified pressure. Some eductors, such as waterwell eductors, are designed to operate at low pressures, ranging from10 to 50 psig. Eductors used for firefighting purposes normally operate at a medium pressure range, between 140 psig to 185 psig. Chemical ejection eductors used with high pressure sprayers must operate at high pressures, ranging from 1000 to greater than 4000 psig. As pressure increases, flow through a jet or orifice increases. For example, a one inch diameter nozzle will flow 200 gallons per minute (gpm) at a pressure of 45 psig. At a pressure of 180 psig, the flow will double to 400 gpm through the same nozzle.

Eductors are designed to operate effectively within a relatively narrow range of driving fluid pressures and flow rates, and deviation from the design range typically results in substantially reduced performance. For example, a prior art eductor designed to operate with a driving fluid pressure of 150 psig at a flowrate of 277 gpm will lift a column of water 20 feet when operated at those parameters. However, when that eductor is operated with a reduced pressure of 50 psig, with a corresponding flow rate of 162 gpm, the eductor is capable of lifting a column of water about 2 feet.

SUMMARY OF THE INVENTION

The present invention provides an eductor apparatus that overcomes the drawbacks inherent in fixed ratio eductors,and which can be effectively used over a wide range of pressures and flow rates. The multi-stage eductor apparatus of the invention includes a first eductor

The structure and features of the eductor apparatus of the invention will be described in more detail with reference to the accompanying drawing figures.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a side elevation schematic illustration of a first embodiment of the multi-stage eductor of the invention.

FIG. 2 is a side elevation schematic illustration of a second embodiment of the multi-stage eductor of the invention.

FIG. 3 is a graph showing a comparison between the performance of an eductor of the invention and a prior art eductor through a wide range of driving fluid pressures.

FIG. 4 is a side elevation schematic illustration of a third embodiment of the multi-stage eductor of the invention.

DESCRIPTION OF THE INVENTION

The multi-stage eductor of the invention, generally identified by reference number 10, comprises a first stage venturi-type eductor 11, with a venturi throat section 12 and a diffuser section 13, and a second stage venturi-type eductor 14 with a venturi throat section 15 and a diffuser section 16, connected in series with the first stage. The first stage eductor has an inlet 17 and an outlet 18, and the second stage eductor has an inlet 19 and an outlet 20. The inlet of the second stage structure connected to the outlet of the first stage so that the longitudinal axes of the first and second stages are in coaxial alignment. The flow of material into the multi-stage eductor apparatus is indicated as “A”, and the flow of material from the multi-stage eductor apparatus is indicated as “B”. The dashed line through the structure represents the longitudinal axis of the multi-stage eductor, as well as the center line of the flow path of material drawn into and through the eductor.

The first stage eductor 11 has a driving fluid inlet 21 for the introduction of a flow of driving fluid indicated as “C”, and the second stage eductor 14 has a driving fluid inlet 22 for the introduction of a driving fluid “D” to the second stage. The driving fluid(s), or motive fluid(s), is introduced, under pressure, to the respective first and second stage eductors through the respective inlet and is emitted into the interior of that stage through first stage inlet nozzle or nozzles 23 and second stage inlet nozzle or nozzles 24, upstream of the venturi throat of the respective stage. The inlet nozzles are disposed to direct the driving fluid toward the venturi throat at an angle relative to the longitudinal axis of the stage, thereby creating a zone of reduced pressure behind, or upstream from, the inlet nozzles in the region of the suction inlet and inducing material flow into the suction inlet.

The multi-stage eductor of the invention has been demonstrated to provide a dramatic enhancement in eductor effectiveness, measured in terms of the suction, or partial vacuum developed by an eductor apparatus at a selected driving fluid pressure and flow rate. In a controlled comparison test, one of the stages of a multi-stage eductor as illustrated in FIG. 1 was operated at various driving fluid pressures, and the suction created by the single stage during operation at the various pressures was measured. The second stage was then connected to form the two-stage eductor illustrated in FIG. 1, and the suction created by that multi-stage eductor at various driving fluid pressures was measured and recorded. The comparative results are shown in the following table and graphically illustrated in FIG. 3:

The vacuum produced was measured, and is shown in the table, in inches of mercury. Fields in the table for which no data was collected are left blank.

As can be readily seem from the table and the graphical representation, the performance provided by the multi-stage eductor is a dramatic improvement over the performance of a single eductor stage, and is unprecedented in the prior art.

A test of the apparatus of FIG. 1 for the mixing of drilling “mud” was performed to evaluate the performance of the apparatus in a practical application. The apparatus was used to educt AquaGel® dry drilling mud (essentially a bentonite) and mix the dry material with water, which was also used as a driving fluid for the eductor apparatus. Not only did the apparatus of the invention perform more effectively than a conventional eductor in vacuuming the dry material, the shear and mixing of the dry material with water to produce a homogenous drilling mud fluid was highly effective as well. The mud fluid was thoroughly mixed with no clumps of dry material (“fisheyes”), and after a two week period of observation there was no visually detectable precipitation of bentonite particles from the fluid. To determine whether discharging from the multi-stage eductor apparatus of the invention against a static head would effect performance, the apparatus of FIG. 1 was then set up to discharge mixed drilling mud against a 10 foot head, and the results were compared to results obtained without the head. The head pressure or back pressure on the multi-stage eductor had no detrimental effect.

Without limitation to any particular theory or to any particular mechanism of action, it is contemplated that the unprecedented improvement can be attributed to a “drafting effect”, similar to that experienced by a vehicle closely following another in the slipstream created by the leading vehicle. It is known that as a single vehicle, e.g., a race car, travels through the air it creates a zone, or bubble, of high-density air in front of it and a zone of low-density air behind. The difference in the pressure between these two zones of air creates drag, the force that impedes motion. This drag force limits the top speed the car can attain. However, when a second car pulls up behind the first, the slipstreams created by the two merge, so that the first car losses its aft bubble and the second car loses its front bubble. This effect reduces the drag force each car experiences and both are able to travel slightly faster.

The same principle can apply to moving fluids. Again, without limitation as to any particular theory or mechanism, it is contemplated that the fluid discharging from the first stage driving fluid nozzles does not readily give up energy to form a boundary layer on the inner surface of the venturi throat and diffuser. It is contemplated that the driving fluid discharging from the second stage, or downstream, inlet nozzles forms a boundary layer on the inner surface of the second stage venturi and diffuser. The friction, and consequent drag associated with the creation of a boundary layer in the first stage is reduced, if not eliminated entirely.

Returning to the vehicle analogy, if the trailing vehicle drops back out of the low pressure zone behind the leading vehicle, the drafting effect is lost. Likewise, in the case of the multi-stage eductor of the invention, it is contemplated that if the stages are placed too far apart, the first stage cannot draft on the second stage. Although in that instance the second, downstream, stage will reduce head pressure for the first, upstream, stage, the advantage of the drafting affect would be lost. Hence, the stages should be disposed in sufficiently close proximity to take advantage of drafting on each subsequent stage. The close proximity and the drafting effect achieved by the present invention distinguishes it from simply placing separated eductors in series in the flow stream, as has been on occasion done in the prior art. Separated eductors, even though piped in series, do not achieve the drafting effect or the dramatic improvement in effectiveness of the multi-stage eductor of the present invention, and the practice of simply placing eductors in series is not comparable or material prior art to the present invention.

FIG. 2 illustrates a modified version, or second embodiment, of the apparatus shown in FIG. 1. In the apparatus of FIG. 2 the diffuser section 13 of the first stage 11 is removed to enhance velocity and take full advantage of the drafting affect of the fluid entering into the second stage 14. In addition, this configuration places the driving fluid inlet nozzles 23 of the first stage closer to the inlet nozzles 24 of the second stage. The diffuser section 16 of the second stage is retained in order to reduce the velocity of the fluid, thus recovering pressure. The more compact structure of the embodiment of FIG. 2 also provides the advantages of reduced size and weight.

Although the multi-stage eductor of the invention is shown in the drawing figures with two stages, it is to be understood that the invention is not limited with regard to the number of stages. A third stage and/or further additional stages may be added to the apparatus, and the scope of the invention is to be considered to include any number of stages.

The multi-stage eductor apparatus of the invention provide the capability of utilizing different driving, or motive fluids in the different stages. For example, referring to either FIG. 1 or FIG. 2, a first motive supply fluid C, is used to provide a suction for entraining a material A in the first stage 10 a. A second motive fluid D supplied to the second stage 10 b provides drafting affects for entraining and mixing fluids C and D, and material A. The product is discharged through the diffuser 16 of the second stage as a final product B. This capability substantially expands the range of possible uses for an eductor apparatus beyond anything contemplated or possible using prior art apparatus. For example, the multi-stage eductor of the invention is ideally suited for emulsifying a hydrophobic liquid and water with a surfactant.

A further variation, or alternative embodiment of the multi-stage eductor of the invention is illustrated in FIG. 4, in which the motive fluid C for the first stage is introduced through a jet nozzle disposed with its axis in alignment with the longitudinal axes of the first and second eductor stages, to create a drafting envelope as generally indicated in the figure. As material A is introduced into the first stage it is entrained in the motive fluid through the first stage of the apparatus and into the second stage. The embodiment of FIG. 4 provides the same capabilities and advantages as the previously described embodiments, and is susceptible to the same wide range of uses.

Another ideal application for the present invention is for emulsifying super absorbent polymers (SAP) into water. Super absorbent polymers, which readily absorb liquids, are used in baby diapers, as well as many other uses. The typical SAP is the chemical polyacrylamide, which is normally supplied in a prehydrated form. Thus, prehydrated or prehydrolyzed polyacrylamide is given the acrynom PHPA. Polymers are coiled when in the prehydrated state. Thus, the polymer must be uncoiled and aged to be highly effective. The multi-stage eductor allows for pneumatic conveying PHPA into the first stage for uncoiling purposes, followed by thorough mixing and blending in the second stage. The PHPA emulsion can then be used for water treatment purposes, as a drilling fluid additive or as a firefighting agent.

The multi-stage eductor can also be utilized as an effective firefighting tool. Aqueous film forming foam (AFFF) is utilized to suppress Class B fires. AFFF is educted into the firefighting water and sprayed on top of the pool of burning fuel. Also, it may be sprayed on a pool of spilled fuel to prevent a fire or to prevent reflash of a fire. The benefit of the multi-stage eductor is that is can supply high pressure water similar to a firefighting monitor, while simultaneously educting in the AFFF.

Another application for the multi-stage eductor can be found in the wastewater treatment industry. Aerators are used to supply dissolved oxygen to aeration lagoons, ponds or tanks. Aerators range from propeller type systems to low pressure roots blowers to ineffective conventional eductor systems. The multi-stage eductor is very well suited for a wastewater treatment plant for several reasons. First, it can be used to entrain air and discharge the mixture to the bottom of the lagoon. This agitates the lagoon and prevents settling of solids. Second, since the multi-stage eductor will pull a high vacuum, a suction hose can be attached to the multi-stage eductor. This allows for operating the eductor of the invention as a mini-dredge. Thus, solids can be removed from the bottom of the lagoon for cleaning purposes with a multi-stage eductor that can also be used as an aerator.

Another potential use for the multi-stage eductor of the present invention involves the capture and recovery of volatile organic compounds (VOCs); a use to which conventional eductors have never been put. With the multi-stage eductor of the invention a deep vacuum can be drawn on, for example, a glycol recovery boiler condenser in order to recover VOCs. The vacuum and the flow rate of VOCs can be controlled by operating each stage independently of one another. For example, if the motive fluid is natural gas and line pressure drops due to unforeseen equipment failures, another stage can be brought online to maintain a constant vacuum and flowrate.

Yet another application for the multi-stage eductor is using it as a venturi scrubber. The variable vacuum and flow rate capabilities of the multi-stage eductor, coupled with its ability to thoroughly shear and mix fluids with micron sized particles, makes it a highly effective gas scrubber. Themulti-stage eductor would be ideally suited for scrubbing particulate matter smaller than 2.5 microns (PM 2.5) from diesel emissions and power plant flue gas.

Another application can be found in the medical industry. Vacuum pumps are used throughout the medical industry for providing a vacuum for many different uses. One application in particular requires the use of an expensive desk size vacuum pump to provide a vacuum for a small size tube of 1 to 3 millimeters in diameter. When an ear is impacted, for example, a physician will utilize a suction tube to withdraw the material away from the eardrum. A small multi-stage eductor can easily be fabricated to operate with water supplied from a lavatory or common kitchen faucet. Typically, most cities control the water pressure between 30 and 60 psig. This allows for a cost effective vacuum pump that is intrinsically safe in that operation does not require electricity.

It is contemplated that many more uses and benefits of the multi-stage eductor will be identified by those of skill in the various arts in which the new apparatus may offer improvement over conventional devices and methods.

The foregoing description of the structure and features, and potential methods of use, of the multi-stage eductor is intended to be illustrative and not for purposes of limitation. The apparatus is susceptible to variations and further alternative embodiments in addition to those discussed above, all within the scope of the invention as described above and set forth in the following claims. 

1. A multi-stage eductor apparatus, comprising a first venturi-type eductor stage having a longitudinal axis, a first stage material inlet centered on said longitudinal axis, and a first stage material outlet in coaxial alignment with said first stage material inlet; and a second venturi-type eductor stage having a longitudinal axis, a second stage material inlet centered on said longitudinal axis, and a second stage material outlet in coaxial alignment with said second stage material inlet, said second stage material inlet connected directly to said first stage material outlet with said longitudinal axes of said first stage eductor and said second stage eductor in coaxial alignment, forming a passageway for the flow of material from said first stage eductor directly into and through said second stage eductor.
 2. The multi-stage eductor apparatus, of claim 1, wherein said first stage eductor comprises a hollow first stage body with open first and second ends and a longutidinal axis extending through said first and second open ends, said open first end of said first stage body being a first stage suction inlet for the introduction of flowable material into said first stage body, having an elongate first stage venturi tube with a hollow interior, open first and second ends and a longitudinal axis, connected at said first end to said first stage body in coaxial alignment therewith, said interior of said first stage venturi tube narrowing in cross-sectional dimension from said first end to a venturi throat and increasing in cross-section dimension from said venturi throat toward said second end, having a first stage driving fluid inlet in fluid flow communication with at least one first stage driving fluid nozzle for directing a driving fluid into said interior of said first stage venturi tube adjacent to said first end thereof in the direction of said second end of said first stage venturi tube.
 3. The multi-stage eductor apparatus of claim 1, wherein said second stage eductor comprises a hollow second stage body with open first and second ends and a longutidinal axis extending through said first and second open ends, said open first end of said second stage body being a second stage suction inlet for the introduction of flowable material into said second stage body, having an elongate second stage venturi tube with a hollow interior, open first and second ends and a longitudinal axis, connected at said first end to said second stage body in coaxial alignment therewith, said interior of said second stage venturi tube narrowing in cross-sectional dimension from said first end to a venturi throat and increasing in cross-section dimension from said venturi throat toward said second end, having a second stage driving fluid inlet in fluid flow communication with at least one second stage driving fluid nozzle for directing a driving fluid into said interior of said second stage venturi tube adjacent to said first end thereof in the direction of said second end of said second stage venturi tube.
 4. The multi-stage eductor of claim 1, further comprising a third venturi-type eductor stage having a longitudinal axis, a third stage material inlet centered on said longitudinal axis, and a third stage material outlet in coaxial alignment with said third stage material inlet, said third stage material inlet connected directly to said second stage material outlet with said longitudinal axes of said first stage eductor, said second stage eductor, and said third stage eductor in coaxial alignment, forming a passageway for the flow of material from said first stage eductor directly into and through said second stage eductor and from said second stage eductor directly into and through said third stage eductor. 